Simple and partial implementation of MIME encoding. MIME is covered by
RFC 2045. This library is used by e.g., http_post_data/3 when using the
form_data(+ListOfData) input specification.

MIME decoding is now arranged through library(mime) from the clib
package, based on the external librfc2045 library. Most likely the
functionality of this package will be moved to the same library someday.
Packing however is a lot simpler then parsing.

Pack a number of inputs into a MIME package using a specified or
generated boundary. The generated boundary consists of the
current time in milliseconds since the epoch and 10 random
hexadecimal numbers. Inputs is a list of documents that is
added to the mime message. Each element is one of:

Name=Value

Name the document. This emits a header of the form below. The
filename is present if Value is of the form file(File).
Value may be any of remaining value specifications.

Content-Disposition: form-data; name="Name"[; filename="<File>"

html(Tokens)

Tokens is a list of HTML tokens as produced by html//1. The
token list is emitted using print_html/1.

file(File)

Emit the contents of File. The Content-type is derived
from the File using file_mime_type/2. If the content-type
is text/_, the file data is copied in text mode, which
implies that it is read in the default encoding of the system
and written using the encoding of the Out stream. Otherwise
the file data is copied binary.

stream(In, Len)

Content is the next Len units from In. Data is copied using
copy_stream_data/3. Units is bytes for binary streams and
characters codes for text streams.

Create a MIME header from Attributes and add Value, which can
be any of remaining values of this list. Attributes may
contain type(ContentType) and/or character_set(CharSet). This
can be used to give a content-type to values that otherwise
do not have a content-type. For example:

mime([type(text/html)], '<b>Hello World</b>', [])

mime([], , Parts)

Creates a nested multipart MIME message. Parts is passed
as Inputs to a recursive call to mime_pack/2.

Atomic

Atomic values are passed to write/1. This embeds simple atoms
and numbers.

Arguments:

Out

- is a stream opened for writing. Typically, it should
be opened in text mode using UTF-8 encoding.

bug

- Does not validate that the boundary does not appear in
any of the input documents.